Yoyos and bearings are both not sealed, there is intentionally an air gap between the outer race and the response section, and the shields in a bearing are held in with a shim that has play.
I have pets, I have found pet hair in many “sealed” (read shielded) bearings.
They’re a bit pricy, but if I could afford it, I’d have V shaped ceramic bearings in all of my yoyos. They come unshielded and just a rinse with dish soap and hot water is all they need to get cleaned, and they should never be lubed. Not here to debate the performance of ceramics, but just being able to use soap and water to clean them and having them run exclusively dry is nice. They’re absolutely not for people who prefer a silent bearing though haha. I used to lube my metal bearings slightly after cleaning them in isopropyl alcohol, but once I swapped to ceramics I started running all of my metal bearings dry.
Bearings absolutely get small particles inside and bearing shields do not “seal” them, as people have already stated. I recently went over to using NSK platinums in my favorite throws, and (as also already mentioned) they don’t have shields. They also seem to be extremely sensitive to tiny particles, as they somewhat frequently go from nearly silent to quite loud.
YoyoFriends Philip @Mazdarx7FD posted an extremely helpful bearing maintenance video which has saved me loads of time compared to my previous bearing maintenance routine (soak, dry, lube every time a bearing would get loud). He shows that you can add lube (even way too much), then blow it out with compressed air. I’ve been doing this, or simply use my air compressor to blow out the small particles when it gets loud. Air alone has returned my NSKs to their optimal, near-silent state countless times in <30 seconds. I just thought I would pass along an alternative method to traditional cleaning methods that has worked marvelously for me. Thanks Philip!
Yeah I’ve got a ceramic bearing, I hate its noise at the point that I stopped playing with it at all. 
So, you are thinking that pet hair somehow crept into your screwed-together yo-yo? It id so how?
If people want to fiddle with their bearings; please do so to your hearts content. They will never be better; and will slowly degrade.
To each their own.
You say use better bearings… what about my ds platinum I had to clean?
I have a hard time desheilding bearings more than anything else .
A lot of times I just swap them out save for cleaning later if I ever do it. .
Seems a bit harsh over a friggan bearing guy.
Yeah that was harsh.
Ok, my turn.
What yoyogeezer said sounds like a perfectly good option for anybody that can afford to buy new bearings and have neither the time or inclination to fiddle with ‘the funny ones’.
This all boils down to what you want to spend your time doing and/or what you want to spend your money doing.
Some people try to keep bearings alive because they don’t have the money to buy new ones. Or they do have the money but would rather spend it on something else and are willing to work miracles on the bearings that aren’t cooperating. <> Nothing wrong with that either.
When I was growing up, my older brother and my Dad were both mechanics. I would watch them constantly fixing things that could be ‘fixed’. Not just to save money but because they loved to fix stuff. And…. I joined the same mindset. (The , ‘why get a new one when I can keep this one going’ crowd).
As I got older, I suddenly decided time was more valuable. I was working at a shop and making around $30 an hour. I would calculate how much time and material would be necessary to fix ‘something’, if I had to pay myself to do it? If the number went in the wrong direction, I would just buy a New one.
To some people, keeping bearings alive and functional is fun and rewarding and for those reasons, they choose that option.
If on the other hand, you wake up every morning with 10 tasks to challenge you and you realistically accept you will only be able to get 6 done………. You may just not want to play bearing Paramedic and resuscitate a wonky bearing.
….There is an old saying, ‘You will never be younger than you are today’.
….And obviously any bearing you have will never be newer once you start using it. Especially if you run it dry. Dry bearings are fine if you accept that they will logically wear down/out faster.
Why, you ask? Simple, dry bearings are literally grinding themselves to death. That is just the future of running dry bearings.
Personally, I like dry bearings. But I also understand they will probably have a shorter playing life than even a slightly lubed bearing.
I pretty much remove the shields from almost all the yo-yos I throw. I accept that they will gather string fuzz and worn bearing dust and I am willing to clean them whenever they start to act funny.
That being said, when I have a bearing that just doesn’t want to behave, I will toss it in the trashcan faster than a hick hurls a horseshoe!
This subject should not cause any arguments.
Both diametrically opposite views can be the correct answer.
Some people like to work on bearings to get the most mileage out of them.
And some people just prefer to keep new bearings in the mix and swap them out when necessary.
PS… I think the primary reason Yoyogeezers’ view seemed out of place was because the theme of the thread was ‘How to maintain a bearing’.
So, his buy a New one, response was like posting on a VW forum, ‘How I keep my VW running’… And somebody responds, Just buy a New one’. Lol.
I’m afraid that’s like saying that a high-quality engine should last years without oil changes. It’s simply not true.
As has been pointed out, yoyo bearings are not sealed. None of them are. Sealed bearings have too much drag to work properly in modern yoyos.
I clean my bearings by dropping them into a contact-lens container filled with acetone, closing it up and shaking it for a few seconds. After several cleanings the acetone is contaminated with lots of little black specks that have been flushed out of the bearing. What the contaminants are and how they got into the bearing, I don’t know but they sure are there and after the bearing has been cleaned, it plays like new again.
If you prefer to replace bearings when the performance wanes, that’s your business but some of us prefer to spend a minute or two cleaning the bearing rather than spend money and resources replacing it. You can’t expect us to take your opinion very seriously when we have experienced firsthand the results of simply cleaning a bearing.
Ivan
This is exactly me too 100%
Agree.
However, if one sais “they’re sealed bearing, foreign object can’t go in”, I have to politely let him notice that bearing are not sealed, stuff can go in, and exactly like any other mechanical part they need maintenance. There’s nothing wrong in throw them away and buy a new one. Just in my opinion, buyng a new bearing is more time and money consuming.
I like the contact case idea. I’ve been using one of those little metal tartar sauce dishes, but then I have to swirl it around with a pencil. With the contact case, you can close it, shake it, then open it again. That sounds a lot easier, and I’ve got a bunch of spares from the optometrist. Thanks for the great idea!
This is such an amazing observation.
Danm, I really like the way that you structure your sentences and thoughts. 
